Neurons and Synaptic Transmission Flashcards
Why is neural activity considered an electro-chemical process?
It involves both electrical and chemical elements.
What is the electrical part of neural activity?
The flow of ions (charged particles) in/out of the cell, or through the cell
What is the chemical part of neural activity?
The flow of neurotransmitters between neurons
What are the key ions involved in neurons?
Sodium - Na+
Potassium - K+
Chloride - Cl -
What is a resting membrane potential?
When the neuron is not firing
The difference in charge across the membrane at equilibrium is about -70mV
How many Na+ and K+ ions are inside/outside the neuron at its resting membrane potential?
Inside: More K+ and less Na+
Outside: More Na+ and less K+
*Think of the inside as “less positive” instead of “more negative”.
What are the three stages of computation in the neuron?
Stage 1 - Input Stage
Stage 2 - Processing Stage
Stage 3 - Output Stage
What is a synapse?
Where the axon of one neuron connects to the dendrites of another neuron
Presynaptic Neuron
The neuron BEFORE the synapse
Postsynaptic Neuron
The neuron AFTER the synapse
Synaptic Cleft
Another name for the synapse
How neurons send signals (steps)
- An action potential arrives at the terminal buttons.
- There are vesicles holding neurotransmitters in the terminal button areas of the presynaptic neuron
- These vesicles dock to docking proteins, fuse with the presynaptic membrane, and are dumped into the synapse
- Empty vesicles are recycled through endocytosis of the clathrin-coated pit to take up more neurotransmitters and restart the cycle
How neuron receive signals (steps)
- Neurotransmitters in the synapse dock onto certain ion receptor to either open or close channels
- For an action potential, Na+ channels open and let Na+ into the cell.
- Na+ is positive, and the neuron starts to become excitatory
- Enough of these excitatory postsynaptic potentials add up at the axon hillock until the neuron is depolarized enough (-50mV) and triggers the next action potential to travel down the neuron’s axon
Excitatory Postsynaptic Potential (EPSP)
Cell is less polarized (depolarized) because it has less of a negative charge. This depolarization is excitation because it makes it more likely that the cell will reach the threshold to trigger an action potential. (-50mV)
Inhibitory Postsynaptic Potential (IPSP)
Cell can become more polarized (hyper polarized) so it has a more negative charge.
Hyperpolarization is inhibition because it makes it less likely that the cell will reach the threshold to trigger an action potential
Excitatory Neurotransmitters
Acetylcholine (ACh)
Catecholamines (Dopamine and Noradrenaline)
Glutamate
Serotonin
Inhibitory Neurotransmitters
GABA (Gamma-Aminobutyric Acid)
Glycine
Some Peptides
What is the Processing (or Evaluation) Stage for Neurons?
When information is passed into a neuron from a presynaptic neuron, there are changes in the voltage of the neuron depending on whether the inputs are excitatory or inhibitory.
The inputs are summed together at the axon hillock (spike-trigger zone) to influence the neuron’s voltage.
This will determine if it is enough to trigger an action potential.
To what voltage does the neuron spike during an Action Potential?
+40mV
The Sodium-Potassium pump sends __________ and __________
It sends three Na+ out and pulls two K+ in
What is the purpose of the Na+ - K+ Pump?
To eliminate the excess Na+ ions from inside the cell. These are always sort of working, but more so after an action potential
What is Saltatory Conduction?
In myelinated neurons, the action potentials “jump” from each Node of Ranvier to speed up the transmission of the action potential while maintaining its strength. It’s due to the fact that the action potential does not have to open the ion channels that are in the myelinated sections and they are very well insulated.
Blood Brain Barrier
A lipid bilayer that is described as “semi-permeable” and restricts the diffusion of microscopic objects like bacteria and large hydrophilic molecules in the blood from entering the brain. Allows oxygen, carbon dioxide, and hormones to cross (all hydrophobic)
Types of Glial Cells
Astrocytes
Microglial Cells
Oligodendrocytes
Schwann Cells (peripheral nervous system)
Astrocytes
They create the blood brain barrier. Protect brain from blood borne agents
Plays active role in brain function - respond to and release neurotransmitters/other neuroactive substances
Microglial Cells
Small and irregularly shaped
Phagocytes - devour and remove damaged cells
Oligodendrocytes
Form the myelin sheath in the central nervous system
Schwann Cells
Form the myelin sheath in the peripheral nervous system
Both the intercellular cytoplasm and the extra cellular fluid is made up of ______
Ions
What are spines?
The tiny knobs attached by small necks to the surface of the dendrites where they receive inputs from presynaptic neurons
What are Transmembrane Proteins? Provide examples
They sit upon/through the cellular membrane and allow ions to pass into/out of the neuron. They make the membrane “selectively permeable”.
Examples:
Ion Channels
Ion Pumps
Gated Ion Channels
Ion channels that are capable of changing their permeability for particular ions. They open and close in response to chemical and physical stimuli
Nongated Ion Channels
Ion channels that are unregulated, and always allow the associated ion to pass
Ion Pumps
Enzymes that use ATP (adenosine triphosphate) for energy
They use this energy to actively transport ions across membrane (against concentration gradients)
The Hodgkin-Huxley Cycle
When a neuron becomes more depolarized as Na+ ions pour in, it causes even more Na+ channels to open
Absolute Refractory Period
After the action potential when the voltage-gated Na+ channels are unable to open and no other action potential can be generated
Relative Refractory Period
When the neuron can generate action potentials, but only with larger than normal depolarizing currents
Depolarization is _______ and Hyperpolarization is _________
(Inhibitory or excitatory)
Depolarization is excitatory
Hyperpolarization is inhibitory
